Alkylene oxide derivatives based on tetrahydrofuran copolymers and having the formula R-X, wherein X consists essentially of a copolymer of tetrahydrofuran and a C.sub.2 to C.sub.3 alkylene oxide, R being the radical of a C.sub.8 to C.sub.22 alcohol or carboxylic acid or their oxyalkylation products with from 1 to 20 moles of said C.sub.2 to C.sub.3 alkylene oxide, the total amount of the alkylene oxide and tetrahydrofuran units in R-X being from 60 to 95% by weight and the molar ratio of the alkylene oxide units to tetrahydrofuran units being from 1:0.5 to 1:3. The new products R-X are useful as surfactants, textile auxiliaries and, in particular, emulsifiers in the one-bath finishing and pigment dyeing of textiles.